While a graduate student at Michigan, Dr. Niemann worked with Prof. William Gould Dow (former EECS Professor and Chair) and Prof. Nelson Spencer (former EECS Professor before joining the NASA Goddard Space Flight Center) on the development of the Omegatron mass spectrometer.

"Measurements made by the Omegatron added immensely to knowledge of the upper atmosphere of the Earth and paved the way to mass spectrometric measurements of the planetary atmospheres," stated Dr. George Carignan, Research Scientist Emeritus of the U-M Department of Atmospheric, Oceanic and Space Sciences. Dr. Carignan was a close friend and collaborator of Dr. Niemann's throughout his career.

Dr. Niemann joined NASA Goddard Space Flight Center in 1969 upon graduation. Dr. Nicholas White, Director of Goddard Space Flight Center, called him, "a founding father of atmospheric experiments and mass spectrometry at the center – which ultimately led to the successful SAM experiment currently operating on the Curiosity Rover."2

Dr. White recalled that
early in his career, Dr. Niemann pioneered exploration of the upper atmosphere of the earth, and later focused on planetary atmospheres. He provided the first in situ measurements of the upper atmosphere of Venus on the Pioneer Venus Mission, and later probed the deep atmosphere of Jupiter through his work on the prime instrument on the Galileo Probe.

As a key contributor to the Cassini-Huygens Mission to Saturn, Dr. Niemann helped develop the Cassini Huygens Gas Chromatograph Mass Spectrometer and the Cassini Ion and Neutral Mass Spectrometer. He continued his work at Goddard even after his official retirement in 2007.

Throughout his career, Dr. Niemann maintained a close relationship with the Space Physics Research Laboratory at U-M. Dr. Carignan stated, "His loyalty to Michigan provided space exploration opportunity to a large number of students, and his educational and collaborative association with the Michigan College of Engineering helped to fuel its strong space science and engineering program."

Dr. Neimann received NASA's Distinguished Service Medal for his contributions to mass spectrometry, the John C. Lindsay Memorial Award for Space Science in 1997, and the Al Seiff Memorial Award in 2007 "for outstanding contributions to the understanding of atmospheres of planets or moons through the use of high-speed probes that enter those atmospheres."

Upon hearing of his death, Dr. Niemann's good friend and colleague Jonathan Lunine stated, "He touched so many people scientifically and personally. Hasso's kindness in inviting young people like me to be part of his Huygens GCMS proposal, his exemplary leadership and extraordinary work ethic in making the instrument happen, and his graceful and gracious diplomacy in dealing with the myriad people involved in the project (and difficult ones like me) were all lessons in being a good human being that I will never forget."2